The present vial assembly is generally useful in any analytical test in which activated charcoal is added to a fluid to adsorb a component thereof and is then centrifugally separated from the fluid. The assembly is particularly useful in the technique known as radioimmunoassay wherein an antigen tagged with a radioisotope (e.g. iodine-125, tritium or carbon-14) is added to a vial together with an antibody and a patient's serum containing a competitive antigen. The tagged antigen and patient's antigen will compete for sites on the antibody so that the more antigen of interest there is in the patient's serum, the less radioactive antigen will be bound to the antibody. By adsorbing and separating the unbound antigen, one can measure the radioactivity of the bound antigen to determine the amount of antigen of interest in the patient's serum.
In conducting such tests, the usual procedure is to add to the mixture of serum, antibody and antigen a quantity of specially treated activated charcoal to selectively adsorb unbound antigen. Thereafter, the vial is placed in a centrifuge to concentrate the charcoal at the bottom thereof and an aliquot portion of the remaining fluid is drawn off by pipette or by decanting for measurement of its radioactivity. To facilitate such tests, kits have been provided in which a three component system is used. A pellet of treated charcoal is bonded to the bottom of a first tube while test solution is contained in a capped second tube. After adding serum to the test solution and incubating, the tubes are connected together and shaken whereby the charcoal mixes with the serum mixture and adsorbs unbound antigen. Thereafter, the charcoal is centrifuged back into the first tube and the assembly is carefully tilted to decant the fluid into the second tube. The first tube is discarded and a radioactivity measurement is made on the second tube.
The present invention provides an improved vial assembly which eliminates one of the foregoing tubes and which also eliminates the need for careful handling during decanting. In particular, the present vial assembly consists of an elongate vial open at one end, a cap therefor and treated charcoal in the cap. The cap is formed internally with retention means so as to successively secure, release and secure the charcoal within a compartment defined by the walls of the cap. In one embodiment, the cap is formed with an asperate inner surface to receive and retain the charcoal. In another embodiment, the cap is formed internally with plural protrusions into the cap compartment to retain the charcoal.
In operation, a serum-antigen-antibody mixture is placed in the vial which is then incubated. The cap is then placed on the vial and the assembly is inverted and shaken to mix the contents. The cap vial is then placed inverted in a centrifuge to concentrate the charcoal back into the cap compartment where it is secured by one or both of the above retention means. The assembly can then be simply turned back upright, without any requirement for great care in doing so. The cap (containing the secured charcoal) is then removed and a radioassay determination is made on the fluid remaining in the vial.